<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>固定</title>
    <style>
        body{
             margin: 0;
             padding: 0;
        }
        #box{
            width: 100%;
            height: 50px;
            background: red;
            position: fixed;
        }
        #box .search{
            width: 1260px;
            height: 50px;
            background: red;
            margin: 0 auto;
            line-height: 50px;
        }
        #box .search div{
            float: left;
        }
        #box .font{
            width: 160px;
            height: 50px;
            font-size: 20px;
            color: white;
            line-height: 50px;
        }
        #box .search div input{
            width: 640px;
            height: 30px;
            border: none;
            outline: none;
            padding-left: 8px;
        }
        #box .search div button{
            width: 90px;
            height: 32px;
            border: none;
            background: red;
            color: white;
            font-size: 15px;
        }
        #box .search div button:hover{
            cursor: pointer;
        }
        #big{
            width: 100%;
            height: 9000px;
            background:yellow;
        }
    </style>
</head>
<body>
    <div id="box">
        <div class="search">
            <div class="font">
                TMALL 天猫
            </div>
            <div>
                <input type="text" placeholder="搜索 天猫 商品/品牌/店铺">
            </div>
            <div>
                <button>搜 索</button>
            </div>
        </div>
    </div>
    <div id="big"></div>
</body>
</html>